Light-Responsive Actuator of Azobenzene-Containing Main-Chain Liquid Crystal Elastomers with Allyl Sulfide Dynamic Exchangeable Linkages

Herein, a light-responsive and light-induced bond-exchange-reaction (BER)-capable actuator of the monodomain liquid crystal elastomer (xMLCE_azo), developed using main-chain mesogenic oligomers containing azobenzene and allyl sulfide linkages, is investigated. Large quantities of the azobenzene and allyl dithiol linkages are incorporated into the main-chain mesogenic oligomer prepared via thiol-acrylate Michael addition polymerization (TAMAP). The xMLCE_azo film is generated via visible-light-induced BER of the drawn polydomain xLCE_azo (xPLCE_azo) film prepared via TAMAP of tetrathiol cross-linkers and diacrylate-terminated mesogenic oligomers. The xMLCE_azo film exhibits large length actuation (38%) through the photothermal effect, along with excellent self-healing and reprogramming properties, under ultraviolet (UV) light irradiation. UV light induced BER of the xMLCE_azo film is used to develop complex-shaped actuators with a bilayer film, containing the xMLCE_azo and xPLCE_azo films, which are bonded by the UV light induced BER without glue. The individual arm of the complex eight-arm flower is remotely actuated under UV light irradiation, and a circular band is rolled under blue laser light irradiation, demonstrating the local remote-controlled actuation and fuel-free motion of the motile soft robot using light irradiation, respectively. Thus, the xMLCE_azo film can be expanded to other interesting applications requiring reprogrammable, self-healing, reprocessable, patternable, and remote-controlled light-triggered elastic, rubber-like actuators.